The present invention pertains to biologically active, polypeptide fragments of mammalian bactericidal/permeability-increasing proteins and methods for making and using said fragments.
Bactericidal/permeability-increasing protein (BPI) is a 50 to 60 Kd protein, isolated from the granules of mammalian polymorphonuclear leukocytes (PMN) which are blood cells that are essential in the defense against invading microorganisms in mammals. BPI occurs only in cells of the myeloid series of blood cells, is produced at the promyelocytic/myelocytic stage of differentiation and is located in the primary granules in these cells.
BPI is a potent bactericidal agent active against a broad range of gram-negative bacterial species. It exhibits a high degree of specificity in its cytotoxic effect, i.e. 10-40 nM (0.5xe2x80x942.0 micrograms), producing greater than 90% killing of 107 sensitive bacteria whereas 100-fold higher concentrations of BPI are non-toxic for other microorganisms and eukaryotic cells. All available evidence suggests that in the intact PMN and in crude leukocyte fractions, BPI is the principal oxygen-independent agent present which is active against BPI-sensitive bacteria.
BPI isolated from both human and rabbit PMN has been purified to homogeneity. The molecular weight of human BPI is approximately 58,000 Daltons (58 kDa) and that of rabbit BPI is approximately 50 kDa. The amino acid composition of these two proteins is closely similar as is the amino acid sequence of their first 15 NH2-terminal amino acid residues. Both proteins are highly basic, having an isoelectric point greater than 9.6.
The biological effects of BPI require attachment of the protein to the surface of the susceptible gram-negative bacteria. Initial binding of BPI to target cells involves electrostatic interactions between the basic protein and the negatively charged sites on the lipopolysaccharides (LPS) on the bacterial outer membrane and leads to an activation of bacterial enzymes that degrade phospholipids and peptidoglycans. The final stage of action is the actual killing of the bacteria by an as yet unknown mechanism. The closely similar amino acid composition and nearly identical bactericidal and membrane-perturbing properties of BPI purified from human and rabbit PMN suggest that this protein has been highly conserved during evolution and is an important member of the anti-bacterial arsenal of the mammalian PMN.
Due to its potent bactericidal action against gram-negative bacteria and lack of cytotoxicity towards other microorganisms and eukaryotic cells, it is envisioned that BPI may be employed as a chemotherapeutic agent and/or as a model for the design of new antibiotic agents. However, due to its large molecular weight (58 kDa for the human holoprotein), both sequencing and determination of the structural organization of BPI have been hampered (hereinafter the entire BPI molecule is referred to as the holoprotein). The possibility has been raised that, as in the case with other cytotoxic proteins, BPI has a structural organization where the different functions, namely binding, envelope-altering and killing reside in different domains within the BPI molecule. Although BPI fragments, obtained by digestion of the holoproteins with the proteolytic enzyme elastase, has been disclosed (Weiss, J. et al., Clin. Res 34: 537A, 1986), the fragments tested remained associated under the non-denaturing conditions employed. No biological activity was ascribed to any isolated fragments. Moreover, antibodies directed against the holoprotein did not recognize these fragments under denaturing conditions when analyzed using the well-known Western blotting procedure.
Therefore, in light of the above, there is a need in the art for biologically active peptide fragments of BPI for use as bactericidal/permeability increasing agents as well as therapeutic agents. Such fragments are also needed to provide sequence information on BPI to direct the design of future generations of antimicrobial agents specific for gram-negative bacteria and to be used as probes into the molecular organization of the holoproteins.
It is an object of the present invention to provide biologically active peptide fragments of mammalian BPI.
Another object of the present invention is to provide biologically active peptide fragments of mammalian BPI with improved antimicrobial effectiveness.
Yet another object of the present invention is to provide a process for the production of biologically active peptide fragments of mammalian BPI.
Yet another object of the present invention is to provide methods for treating mammals suffering from infections caused by gram-negative bacteria.
A further object of the present invention is to provide a method for increasing the permeability of gram-negative bacteria.
A still further object of the present invention is to increase the effectiveness of gram-negative bactericidal agents.
These and other objects of the present invention will be apparent to those of ordinary skill in the art in light of the present description, accompanying claims and appended drawings.
The present inventors have unexpectedly discovered biologically active fragments of mammalian BPI substantially shorter in length than the native BPI protein. Although these fragments are substantially smaller than the native molecule, they retain at least substantially all of the bactericidal and permeability-increasing properties of the intact protein.
The biologically active BPI fragments of the present invention can be produced by incubating a sample comprising the BPI holoprotein under BPI cleaving conditions and recovering biologically active fragments of the BPI holoprotein. The preferred BPI cleaving conditions include heating of the BPI holoprotein in an acceptable buffer for a time ranging between about 16 and 24 hours at a temperature between about 20xc2x0 C. and about 37xc2x0 C.
In another aspect, the present invention provides a method for treating mammals suffering from infections caused by gram-negative bacteria comprising administering to mammals in need of such treatment a gram-negative bactericidal-effective amount of at least one of the above-mentioned biologically active BPI fragments.
In another aspect, the present invention provides pharmaceutical formulations for treating infections in mammals caused by gram negative bacteria comprising a gram-negative bactericidal-effective amount of at least one of the biologically active BPI fragments or pharmaceutically-acceptable salts thereof.
In yet another aspect, the present invention provides a method for increasing the permeability of gram-negative bacteria comprising incubating the bacteria with a gram-negative-bacterial-permeability-increasing-effective amount of a biologically active fragment of BPI.
In still another aspect, the present invention provides a method for increasing the effectiveness of gram-negative bactericidal agents in mammals in need of such treatments, comprising co-administration of such agents with the biologically active fragments of BPI.
A still further aspect of the present invention is directed to a purified, isolated DNA sequence having the sequence set out in FIG. 5 or its complementary strand and DNA sequences hybridizing under stringent hybridization conditions with said DNA sequences. The DNA sequence encodes the human bactericidal/permeability-increasing protein.